This invention relates to a member comprising fibers, to a composite article reinforced with fibers, and to a method for making such member and article. More particularly, in one form, it relates to a fiber reinforced composite article that, during service operation, experiences concurrently a plurality of temperatures and stresses varying between a plurality of regions of the article.
In power generation apparatus, for example a gas turbine engine, wide variations in operating temperatures are experienced from inlet to exhaust, as well as across or within individual components of such an engine. An example of such thermal variation has been observed within the engine exhaust system across or within regions of panels such as exhaust flaps. Another example is a turbine engine blading component, such as a blade, vane, strut etc., having a surface or skin region that experiences a temperature greater than does reinforcing or strengthening spars in the component.
Such high thermal gradients across or within such an article or component or within a region, sometimes called a hot spot, of the article has generated relatively high thermal strains sufficient to limit the operating capability of the article. For example, cooler edge regions of a gas turbine engine exhaust flap, made of a high temperature oxide fiber reinforced ceramic matrix composite material, existing concurrently with a higher temperature region within or away from the edge regions, have been observed to develop cracks that can decrease the operating life of the article. Such degradation is believed to result from the inability of the reinforced structure of an article, made generally from a single kind of material, to compensate for different stress levels developed from a stress conflict between different temperature regions. The reinforced matrix of the composite including reinforcing fibers, for example of a single kind, alone does not have the capability to withstand or compensate for such wide strain variations across the operating temperature range of the article.